A piezoelectric thin film bulk acoustic wave resonator generally includes a piezoelectric thin film deposited by a thin film forming apparatus, and a resonator unit composed of a first metal electrode film and a second metal electrode film, which are located above and below while sandwiching at least a part of the piezoelectric thin film. The first metal electrode film functions as a lower electrode, and the second metal electrode film functions as an upper electrode. The piezoelectric thin film is polarized in the thickness direction. An alternating electric field generated by alternating voltage that is applied between the lower electrode and the upper electrode causes stretching of the piezoelectric thin film in the thickness direction, namely an acoustic wave by piezoelectric/anti-piezoelectric effects.
There exist acoustic insulating layers above and below the resonator composed of the piezoelectric thin film, the lower electrode, and the upper electrode. The piezoelectric thin film bulk acoustic wave resonator suitable for a high frequency filter is classified based on methods by which a bulk acoustic wave is sealed inside the piezoelectric thin film, and FBAR (Film Bulk Acoustic wave Resonator) and SMR (Solidly Mounted Resonator) are well known. An interface between a solid body and gaseous matter (or, vacuum) functions as an effective acoustic insulating layer, and therefore areas above and below the resonator are in a gaseous state (or, vacuum state) in FBAR. An area above the upper electrode is in a gaseous state (or, vacuum state), and a Bragg reflector is mounted below the lower electrode in SMR.
U.S. Pat. No. 6,496,085 B2 discloses the device configuration of SMR and a process flow thereof. Japanese Patent Application Laid-Open No. 2005-303573 proposes a resonator structure in which AlN is formed only on a lower electrode and no bump is formed on an upper electrode due to AlN high orientation. Further, US 2005/0248232 A1 describes an improvement of AlN orientation by sequential deposition of a lower electrode and a piezoelectric film, and an electromechanical coupling coefficient. The above US 2005/0248232 A1 describes that flatness and cleaning properties immediately after deposition are not maintained on a surface of the lower electrode due to adsorption of impurities in conventional piezoelectric film manufacturing process ([0008]).
Further, Japanese Patent Application Laid-Open No. 2004-200843 discloses a manufacturing method which aims at reducing a cost in such a manner that a support film is made of AlN, and a sacrificial layer for forming an oscillation space, the support film, a lower electrode film, a piezoelectric thin film, and an upper electrode film are sequentially deposited in the same apparatus.
Further, “Comparison of Micromachined FBAR Band Pass Filters with Different. Structural Geometry” (Park et al, 2003 IEEE MTT-S Digest, pp. 2005-2008) discloses the device configuration of FBAR and a process flow thereof.
On the other hand, a thin film tuning-fork-shape distorting oscillator is composed of, as similar to the piezoelectric thin film bulk acoustic wave resonator, a piezoelectric thin film deposited by a thin film forming apparatus, and a first metal electrode film and a second metal electrode film which are located above and below while sandwiching a part of the piezoelectric thin film, and is a distorting oscillator in which the piezoelectric thin film is patterned in a tuning-fork shape.
U.S. Pat. No. 7,083,740 B2 discloses the resonance device configuration of a thin film tuning-fork-shape distorting oscillator and a manufacturing method thereof.